This invention relates to optical amplifiers, and more particularly to optical amplifiers which provide a relatively constant optical output power over a wide range of optical input powers.
An optical limiting amplifier (OLA) that has a relatively constant optical output power for a wide range of optical input power variations is required for many practical optical network applications such as optical transmission and distribution networks. For example, OLAs with a large dynamic range can be used as a power amplifier, an in-line amplifier, or a pre-amplifier in a telephone subscriber loop or a long-haul system, where distribution and/or transmission losses vary significantly from location to location. In addition, OLAs can be used to equalize the unequally received optical power from different terminals in an optical switching network.
Prior art optical amplifiers do not have the necessary high power output over a wide operating range needed for these applications. For example, prior art erbium-doped fiber amplifiers (EDFAs) provide only soft limiting of the input power applied to them. Thus, for low input powers the amplifier produces only a small output power. For the applications described above, however, hard limiting is required to achieve a high gain constant output power over a wide range of input powers.